The present invention relates to an injection molding apparatus for forming plastic articles. More particularly, the present invention relates to a stack mold apparatus having an insulated runner configuration and an automatic system for ejecting the runner for color or resin changes.
Molding apparatuses for delivering molten plastic material to a mold space are known in the art. Those having insulated runners are particularly well known in the art. In fact, they are the forerunner of today's hot runner molding systems. Seymour U.S. Pat. No. 3,023,458 illustrates one such early hot runner mold system. In this system, a gate for providing plastic material to a mold space is opened by a valve stem that is pushed back by virtue of the injection pressure of the plastic material pushing on a shoulder of the stem. When this pressure is removed, the valve stem is moved to a closed position by a spring. Channels for carrying heating devices are provided in close proximity to the runner cavity so as to keep plastic material in an inlet chamber heated.
Peters et al U.S. Pat. No. 3,093,865 illustrates an early insulated runner system in which there is an insulating thermoplastic layer adjacent the walls of the runners and an inner molten thermoplastic material. This system also includes two plates which can be separated to allow ejection of the runner during resin changes. Latching means in the form of a bolt are used to hold these plates together and facilitate separation. Heated probes are used in the system's nozzles so as to allow interruptions in the molding operation for a period of time equal to the maximum time the plastic material will remain molten in the runner.
Perras U.S. Pat. No. 3,591,897 illustrates a runnerless mold system useful for the injection molding of thermoset plastics. The mold features mechanically separable parts or subassemblies for opening and closing the mold. The mold also has thermodynamically isolated regions or zones whereby curing heat is supplied to the mechanically separate parts which define the mold cavity, and cooling or lesser heat is provided for the sprue and runner system to assure non-curing conditions for injected plastic that has yet to reach the cavity regions. The sprue-and-runner system includes a specially cooled secondary sprue associated with each independent mold cavity.
The use of heated probes in combination with hot runners or insulated runners is also well known in the art. Robinson U.S. Pat. No. 3,103,039, Whitney U.S. Pat. No. 3,189,948, Drazick U.S. Pat. No. 3,758,248 and Crandell U.S. Pat. No. 3,970,821 exemplify such combinations. The heated probes are used primarily to maintain the temperature of the material flowing through the sprue and/or runner system during injection into a mold or die.
Segmuller U.S. Pat. No. 3,537,139 relates to an injection nozzle arrangement for a hot channel injection molding device which comprises a heated distributor plate means, a mold portion cooperating with the heated distributor plate means and means providing at least one delivery channel for the injection molding material. Each delivery channel incorporates a recess which is partially formed in the heated distributor plate means and partially in the mold portion. The mold portion is provided with a number of injection openings corresponding to the number of delivery channels. The arrangement further includes the provision of at least one heat conducting core located internally of each delivery channel and extending at least throughout a portion of the length of the delivery channel substantially coaxially with respect to and into the associated injection opening. Each such heat conducting core being in a heat conducting relationship with the heated distributor plate means.
Kessler U.S. Pat. No. 3,776,676 and German Offenlegungsschrift 3,504,816 to Hemmerich illustrate systems having insulated runners. The Kessler patent illustrates an insulated runner used in combination with cold sub-runners. The German Offenlegungsschrift to Hemmerich shows an insulated runner for two resins injected simultaneously through a common nozzle. The runners are formed between a number of different plates.
It is also known in the art to provide hot runner systems with a latching device which provides access for removal of the complete hot runner system. Savory U.S. Pat. No. 3,669,596 illustrates one such system. In the Savory system, a bolt is used to lock two die parts together to permit inspection and cleaning of the injection nozzle.
Sorenson U.S. Pat. No. 4,427,618 shows an insulated runner multicavity injection molding apparatus. The invention described in this patent is directed to injection molding a product in such a manner that the angle of the inclination to the injection point of the surface of the product is between 0.degree. and 90.degree.. In this system, the insulated runner has gating points on the sides of the parts being formed. The insulated runner is formed between the faces of two plates which separate along a plane perpendicular to the clamping direction.
Insulated runners have been used in the past because they provide superior streamlining of the runners so that there is less degradation of material when compared to the plastic material in the channels of a hot runner manifold. Insulated runners allow faster changing of resins because the entire runner system can be removed. It does not have to be purged like a hot runner.
Stack mold systems are also well known in the art. Teraoka U.S. Pat. No. 3,663,145 and Koch et al. U.S. Pat. No. 4,249,882 illustrate stack molds with a cold runner system which can be ejected on each molding cycle. A special machine with an extruder/injection unit mounted on the side of the mold is required to run the mold.
Bielfeldt et al. U.S. Pat. No. 3,843,294 also shows a stack mold system. In this system, there is a centrally heated sprue that remains heated throughout the cycle. The mold is used for forming parts having holes in them, such as records or discs. There is however, no runner system in that the resin is delivered directly from the heated sprue.
Swedish Patent 7810352-0 to Somberg illustrates a stack mold for processing elastomeric resins, i.e. those that remain flexible even after cooling. The mold ejects a cold runner system during every cycle at the same time the parts are ejected. A special mechanism is provided in the mold for automatically ejecting the runner. This mechanism includes a complicated linkage and hinge system for swinging the mold plates aside to allow a sleeve to strip the runner from a vertical pin around which it is formed during injection. As a result of this construction, the mold requires a lengthy opening stroke and a long mold open time to achieve ejection of the runner. Both factors are quite detrimental to cycle time and complication of the mold construction.
Accordingly, it is an object of the present invention to Provide an improved injection molding apparatus having an automatic ejection system for ejecting the runner.
It is a further object of the present invention to provide an apparatus as above which is relatively simple in construction and in use.
It is a further object of the present invention to provide an apparatus as above which makes use of an insulated runner system to prevent degradation of the plastic material.
These and other objects and advantages will become more apparent from the following description and drawings in which like reference numerals depict like elements.